This invention relates generally to electrodes on which semiconductor wafers are clamped and that have cannelures against the backsides of the wafers, and more particularly to using such cannelures to provide for detection of wafer shift of the wafers when the wafers are clamped to the electrodes.
Electrodes area used in a variety of different semiconductor fabrication processes. Typically, a semiconductor wafer is clamped to an electrode, and the backside is exposed to a gas, such as helium, through a cannelure, or groove, in the electrode. The gas ensures that there is a uniform thermal media throughout the semiconductor fabrication process being performed. In some semiconductor fabrication processes, the frontside of the clamped semiconductor wafer is exposed to plasma, as is the case in various dry etching semiconductor fabrication processes.
FIG. 1 shows a side cross-sectional view of a typical system 100 in which a semiconductor wafer 112 is clamped to an electrode 106, via a clamp 104. The electrode is situated within a ring 102. The clamp 104 and the ring 102 may have various holes for mounting and other purposes that are not shown in FIG. 1. The cannelure 110, or groove, within the electrode 106, faces the backside of the semiconductor wafer 112. Holes 108 connected to the cannelure 110 allow for a gas to be piped in, and to which the backside of the semiconductor wafer 112 is exposed. On the frontside of the wafer 112, the wafer 112 may be exposed to plasma in certain semiconductor fabrication processes.
A problem that can occur within the system 100 of FIG. 1 is that the semiconductor wafer 112 shifts even though it is clamped by the clamp 104. For instance, the wafer 112 may rotate, change orientation, or tilt, among other different kinds of shifting. Such shifting can likely expose the electrode 106 to the plasma or other material to which the frontside of the wafer 112 is being exposed. This is shown in FIG. 2, which is a top view of the system 100, in which some components of the system 100 have been omitted for illustrative clarity.
In FIG. 2, the semiconductor wafer 112 has rotated to the right within and relative to the clamp 104, as indicated by the arrow 202. Thus, the flat 204 of the semiconductor wafer 112, which should be aligned to the bottom of the clamp 104, over the flat 206 of the electrode 106, has instead rotated to the right. As shown in FIG. 2, this exposes the electrode 106. In the case where the frontside of the wafer 112 has been exposed to plasma, this means that this part of the electrode 106 has also now been exposed to plasma.
Such plasma exposure of the electrode 106, however, can have disadvantageous consequences. Arcing may result, potentially damaging the electrode 106. Furthermore, the arcing may cause undesired particles to be formed on the semiconductor wafer 112, which can decrease semiconductor device yield, and also cause wafer scrap. Wafer scrap and reduced device yield are costly to the semiconductor foundry fabricating the devices, especially when it cannot pass these costs along to the customer.
Therefore, there is a need for semiconductor wafer shift detection when the wafer has been clamped to an electrode having a cannelure that exposes the backside of the wafer to gas. Such detection should be sensitive and fast enough to detect wafer shift before the electrode has a chance to arc, in the case where the frontside of the semiconductor wafer is exposed to plasma. For these and other reasons, there is a need for the present invention.
The invention relates to a backside cannelure of an electrode to provide for detecting semiconductor wafer shift after the wafer has been positioned over the cannelure of the electrode. The wafer has a backside and a proper position over the cannelure. The cannelure exposes the backside of the wafer to a gas piped in through one or more holes of the electrode. The cannelure has a size such that deviation of the wafer from its proper position by more than a threshold partially exposes the cannelure, such that the gas leaks from the cannelure as now partially exposed. A gas flow detector may detect the gas leaking from the cannelure, and provide corresponding detection of the wafer deviating from its proper position.
Embodiments of the invention provide for advantages over the prior art. Sizing the cannelure so that the cannelure is exposed when the semiconductor wafer deviates from its proper position causes gas to leak through the cannelure. A backside gas flow detector detects this increased flow of gas, such that it can be concluded that the semiconductor wafer has shifted. Power to the electrode can then be disconnected before arcing occurs, preventing damage to the electrode or the semiconductor wafer. That is, the gas detection is fast and sensitive enough to prevent such electrode and/or wafer damage. Still other advantages, aspects, and embodiments of the invention will become apparent by reading the detailed description that follows, and by referring to the accompanying drawings.